diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index eb8aa142..05c8848b 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -68,6 +68,14 @@ edge planes); (2) retail tokens 1093–1107: two look-in floods acdream never en
 the FW0 `Doorway_still_first_frame_diff` was a diff printer, never an exact pin), now
 exposed by the eight-kind comparison. Signature lengths: retail 1185 tokens, acdream 1170.
 
+**Z-range note (2026-09-03):** the block's z slab is NOT the difference — retail pads
+`max_zval = Land_Height_Table[max] + 200`, `min_zval = table[min] − 1` (`CLandBlock` @0x0052f297/
+0x0052f2aa) and BOTH acdream paths mirror it (`LandblockBuildFactory.ComputeWalkZSlab` for
+production, `WalkLandscapeDatBuilder` for the replay). Remaining suspects for the `a9c9`
+admission: the per-view block edge-plane test (`WalkVisibilityMath.BlockCheck` against
+`LScape::draw_check_blocks` @0x00505f80's clip-height grid — BN elides the 192 m block
+interval to `0f` there) and the exit-view union at this pose (two surviving views).
+
 **Degrade note (2026-09-03 review):** the FW0 sibling row for the SAME pose pins
 `RetailFrameWalk.DegradeMultiplier = 0f` because that capture ran under cdb load with
 `Render::deg_mul` depressed; the OH doorway capture also ran under cdb, so check the